It is becoming increasingly desirable and necessary to replace or reline metallic gas and water pipes with plastic pipes that are lighter, less susceptible to corrosion and easier to handle and manipulate. Indeed, various regulations and legislation set out strict rules and conditions regarding the nature of pipes that are situated in and around domestic buildings. For example, within UK houses there is the requirement that gas must be contained within pipes having a metal sheath.
In some circumstances, old underground metal pipes are simply dug up to be replaced with plastic counterparts (using “open-cut” techniques). In other situations, where it is desirable, necessary or simply more convenient to leave the metallic pipes in place, they are relined with a plastic pipes. The process of relining a metal pipe with a plastic one has several advantages over replacing the metal pipe entirely with a plastic one. In particular, the new plastic pipe can be threaded through the existing metal pipe thereby negating the requirement to dig up the old pipe and install and set the new one. Of course, this method is more cost effective, in addition to being more convenient.
However, it is found that the introduction of a lining pipe having a smaller diameter than the host pipe, leads to an inevitable increase in head loss. Head loss is the fluid pressure lost along a length of pipe due to friction. It is directly proportional to the length of the pipe and inversely proportional to the diameter of the pipe. Therefore, the longer and narrower a pipe is, the greater the head loss will be.
In the gas industry, ¾″ [19 mm] diameter metallic service pipes are typically relined with 16 mm diameter polyethylene (PE) pipes (where diameters are approximate inner diameters). The length of the 16 mm PE pipe is generally not limited and so the head loss incurred in these installations is often excessive. The potential for excessive head losses has led to the prohibition of such practice in some areas, leaving expensive open cut techniques as alternatives.
Other problems are associated with providing an effective and adequate joint from the new plastic service pipe to a fitting, such as a valve or meter, for example. These so-called service head adaptors are well known in the prior art, and a sample of which is described below.
The Draw Lock® Service Insertion Adaptor by Georg Fischer Fittings (www.fittings.at) provides a fitting that attaches to the end of a steel stand pipe having a PE interior lining pipe. The fitting allows the service pipe to be connected to a domestic fitting such as a meter. To seal the service insertion adaptor to the end of the service pipe, the user first inserts the adaptor over the PE pipe and then screws it tightly on to the steel riser. The PE pipe extending from the top of the adaptor is then cut flush with the top of the adaptor. A copper liner, expander and adaptor bush is assembled onto a draw tool and then inserted into the bore of the PE pipe until the adaptor bush rests on the top of the service insertion adaptor. The user then uses a spanner to rotate the draw tool relative the adaptor. The expander, which is a conical nut, moves through the copper liner and expands it forming a joint. The draw tool, expander and adaptor bush are then removed leaving the expanded copper liner in place within the PE pipe. The fitting and PE pipe are then sealed with respect to the steel stand pipe allowing a meter control valve, for example, to be installed.
Another type of adaptor is the Serviflex® Service Insertion Adaptor, also by Georg Fischer (www.fittings.at). This adaptor is specifically designed for use with steel pipes that are lined with Serviflex® pipes provided by Radius Systems Limited. To install the Serviflex® Service Insertion Adaptor to such a pipe, the Serviflex® pipe must first be cut so that 6″ (150 mm) protrudes from the steel service pipe. An adaptor body is then fitted to the steel service pipe and a seal and washer are inserted over the Serviflex® pipe and into the adaptor body. The washer has a “lug” that protrudes radially from it that fits into a complementary groove in the adaptor body to prevent rotation therebetween. The Serviflex® pipe is then cut just above the top of the adaptor body before a metallic insert is inserted into the end of the Serviflex® pipe. A fire resistant washer is then placed on top of the adaptor body and a nipple is tightened down onto the body compressing the fire resistant washer. The downward moving nipple causes the washer to move downwards compressing the seal below causing it to deform radially inwards against the Serviflex® pipe and insert. The washer is prevented from rotating within the adaptor body and so only moves downwards against the seal, thereby not transmitting any rotational movement to the seal or the Serviflex® pipe. The Serviflex® Service Insertion Adaptor does not require any specialist tooling for installation.
Similarly, the Live Insertion Service Adaptor from WASK-RMF (http://www.wask-uk.com/) does not require a specialist tool to make a connection with a service pipe and relies on a compression fitting. The WASK-RMF Live Insertion Service Adaptor comprises a body that is slid over a lining pipe of a service pipe and screwed onto the surrounding metallic pipe. A copper insert is slotted into the open end of the lining pipe and a nipple is screwed axially into the body using an appropriately sized spanner. The axial movement of the nipple causes a captive olive, within the body, to compress radially and tighten against the lining pipe. The captive olive has a serrated inner surface that engages with the lining pipe.
In the document WO-A-2008/107680 (Corus UK Limited), a compression fitting is described for connecting steel pipes as a first fit device. The Corus device has a housing with a bore for receiving a steel pipe, where the bore is provided with a seat. A deformable sealing ring sits on top of the seat beneath a washer and a grip ring. To establish a sealed connection with the steel pipe, a nut is screwed onto the assembly. The nut has an internal taper that abuts the grip ring and urges it radially inwards against the surface of the steel pipe. The grip ring comprises sharp teeth that project radially inwards that bite into the surface of the steel pipe. Screwing the nut further pushes the grip ring axially down onto the washer and the sealing ring. Since, at this point, the grip ring is biting into the surface of the steel pipe, further rotation of the nut causes the pipe to move axially. In addition, the rotating nut will exert a torque on the grip ring and therefore on the pipe. The axially moving grip ring and washer causes the sealing ring to become compressed between the washer and the seat and deform to form a seal.
It is an object of the present invention to provide an improved adaptor for producing a seal at the end of a service pipe that has a lining pipe, where no additional tools are required to fit the adaptor, and the seal is efficient and effective whilst minimising the risk of pipe failure. In particular, it is desirable to form a secure joint between the adaptor and the lining pipe without using excessive forces, thereby not compromising the integrity of the lining pipe. It is also particularly desirable that substantially no rotational forces are transmitted to the lining pipe when establishing a secure sealed connection.
In some cases, it may be desirable to electrically isolate the metallic host pipe from an auxiliary pipe system. In particular, in domestic gas systems, it is desirable to have the system electrically isolated. Indeed, in certain jurisdictions, it is a regulatory requirement that the metallic service pipe is electrically isolated from the auxiliary pipe system.
Current methods for isolating a domestic gas system involve fitting a specialised piece of apparatus in between the service head adaptor and the domestic gas system where the specialised apparatus comprises at least one electrically insulating component. In practice, the use of an additional piece of apparatus for electrical isolation is inconvenient (and in many cases impractical), whilst adding to the complexity of connecting a service pipe to a domestic pipe system and increasing the number of potential leak paths.
It is therefore a further object of the present invention to provide a more convenient and robust way of electrically isolating an auxiliary pipe system from a service pipe when making a connection therebetween.